Bright, safe X-ray

doi:10.1038/nindia.2011.12 Published online 31 January 2011

New research has shown that focusing ultrashort pulses of a femtosecond laser onto a copper surface coated with multiwalled carbon nanotubes (MWNTs) can produce intense hard X-rays with low ion debris. Such hard X-ray sources have a variety of applications in imaging, lithography, microscopy and materials processing.

The researchers used carbon nanotubes, which, when coated on a surface, generate ultrashort electron bunches that produce hard X-rays. They focused ultrashort pulses of a femtosecond laser onto two surfaces: a MWNT-coated copper surface and a bare polished copper surface. The intense, ultrashort laser pulses instantly ionize the solid target, creating hot electrons that ultimately release energy in the form of X-rays.

The experiments revealed that the MWNT-coated surface produced an X-ray flux that was two orders of magnitude more intense and with three orders of magnitude better suppression in ion debris than the polished copper target.

The researchers explain the enhanced X-ray emission by an enhancement of local electric fields at the nanotubes. "Our study offers clear pointers to the optimization of the physics for generating hotter plasmas and enhancing photon emissions from dense plasmas excited by femtosecond, high-intensity lasers," says lead researcher G. Ravindra Kumar.

The authors of this work are from: Tata Institute of
Fundamental Research, Mumbai, and Advanced Centre of Research in High
Energy Materials (ACRHEM), University of Hyderabad, Hyderabad, India,
Department of Physics and Astronomy, Clemson University, Clemson, South
Carolina, USA and Department d'Optique P. M. Duffieux, Institut
FEMTO-ST, Universite de Franche-Comte, Besancon, France.